What is shale made of?

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Shale is made of silt and very fine minerals that settle to the bottom of a body of water to form a laminated rock. The materials that form silt are the same that form mud. While shale is a mudstone, the laminates create fissures that differentiate it from other mudstones.

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Crushing shale forms raw material for other uses, such as making brick. However, organic black shale often forms petroleum or natural gas. The black color of this shale is from the organic particles that settle into the shale as it forms. The sun warms this buried organic material, transforming it into an important energy source. Black shale almost always contains organic material and forms underwater. The water protects the organic material from oxygen, so it burns readily.

Sandstone draws out of the shale below it for deposits that wells easily retrieve. However, as of 2014, this easy-to-gather source of petroleum is in short supply. Drillers sometimes turn oil wells horizontally once they reach a narrow shale layer, allowing more effective collection of the oil. A second method of collection involves pumping saltwater into the well to force the oil out of the shale and into the pump. The process is hydraulic fracturing.